Rankine cycle apparatus

ABSTRACT

When a flow of a working medium stagnates in an expander or evaporator of a Rankine cycle apparatus including a closed working medium circulation circuit, a high pressure exceeding an allowable maximum pressure level of the expander or evaporator is produced within the closed working medium circulation circuit. In such a case, the water-phase working medium is first discharged via relief valves out of the circulation circuit, so that the pressure within the circulation circuit can be lowered. Then, once vapor within the evaporator, having been lowered in temperature and pressure, flows backward within the closed working medium circulation circuit, the vapor is also discharged via the relief valves out of the circulation circuit. In this way, the pressure within the expander or evaporator can be reliably prevented from exceeding the allowable maximum pressure level.

FIELD OF THE INVENTION

The present invention relates generally to Rankine cycle apparatus, andmore particularly to a Rankine cycle apparatus which is used, forexample, as a vehicle-mounted apparatus for converting exhaust heatenergy of a vehicle-mounted engine into mechanical energy.

BACKGROUND OF THE INVENTION

Rankine cycle apparatus have been known as systems for converting heatenergy into mechanical work. The Rankine cycle apparatus include astructure for circulating water as a working medium, in the liquid andgaseous phases within a sealed piping system forming a circulationsystem in the apparatus. Generally, the Rankine cycle apparatus includea water supplying pump unit, an evaporator, an expander, a condenser,and pipes connecting between these components to provide circulationcircuitry.

FIG. 19 hereof is a schematic block diagram of a general setup of aconventionally-known Rankine cycle apparatus (e.g., vehicle-mountedRankine cycle apparatus) and certain details of a condenser employed inthe Rankine cycle apparatus. The Rankine cycle apparatus of FIG. 19includes a water supplying pump unit 110, an evaporator 111, an expander107, and the condenser 100. These components 110, 111, 107 and 100 areconnected via pipes 108 and 115, to provide circulation circuitry in theapparatus.

Water (liquid-phase working medium), which is supplied, a predeterminedamount per minute, by the water supplying pump unit 110 via the pipe115, is imparted with heat by the evaporator 111 to turn into watervapor (gaseous-phase working medium). The vapor is delivered through thenext pipe 115 to the expander 107 that expands the water vapor.Mechanical device (not shown) is driven through the vapor expansion bythe expander 107 so as to perform desired mechanical work.

Then, the expanded water vapor is delivered through the pipe 108 to thecondenser 100, where the vapor is converted from the vapor phase back tothe water phase. After that, the water is returned through the pipe 115to the water supplying pump unit 110, from which the water is suppliedagain for repetition of the above actions. The evaporator 111 isconstructed to receive heat from an exhaust pipe extending from theexhaust port of the engine of the vehicle. Among various literatures anddocuments showing structural examples of the Rankine cycle apparatus isJapanese Patent Laid-Open Publication No. 2002-115504.

The following paragraphs detail a structure and behavior of thecondenser 100 in the conventional vehicle-mounted Rankine cycleapparatus, with reference to FIG. 19.

The condenser 100 includes a vapor introducing chamber 101, a watercollecting chamber 102, and a multiplicity of cooling pipes 103vertically interconnecting the two chambers 101 and 102. In the figure,only one of the cooling pipes 103 is shown in an exaggerative manner.Substantial upper half of the interior of each of the cooling pipes 103is a vapor (gaseous-phase) portion 104, while a substantial lower halfof the interior of the cooling pipe 103 is a water (liquid-phase)portion 105. In the vapor portion 104, most of the working mediumintroduced via the vapor introducing chamber 101 to the cooling pipe 103is in the gaseous phase, while, in the water portion 105, most of theworking medium flowing through the cooling pipe 103 is kept in theliquid (condensed water) phase. Boundary between the vapor 104 and thewater 105 (i.e., gas-liquid interface) is a liquid level position 112.

One cooling fan 106 is disposed behind the cooling pipes 103 (to theright of the cooling pipes 103 in FIG. 19). The cooling fan 106 issurrounded by a cylindrical shroud 106 a. Normally, operation of thecooling fan 106 is controlled by an electronic control unit on the basisof a water temperature at an outlet port of the condenser 100. Thesingle cooling fan 106 sends air to the entire region, from top tobottom, of all of the cooling pipes 103 to simultaneously cool thecooling pipes 103.

The condenser 100 operates as follows during operation of the Rankinecycle apparatus. Water vapor of a relatively low temperature, dischargedfrom the expander 107 with a reduced temperature and pressure, is sentinto the vapor introducing chamber 101 of the condenser 100 via thelow-pressure vapor pipe 108 and then directed into the cooling pipes103. Cooling air 109 drawn into the cooling fan 106 is sent to thecondenser 100.

Strong cooling air is applied by the cooling fan 106 to the upstreamvapor portion 104 of the condenser 100, i.e. a portion of each of thecooling pipes 103 where a mixture of the vapor and water exists, andthus latent heat emitted when the vapor liquefies can be recoveredeffectively by the cooling air. Cooling air is also applied by thecooling fan 106 to the downstream water portion 105 of the condenser100, i.e. a portion of each of the cooling pipes 103 where substantiallyonly the water exists. Water condensed within the cooling pipes 103 ofthe condenser 100, is collected into the water collecting chamber 102and then supplied by the water supplying pump unit 110 to the evaporator111 in a pressurized condition as noted above.

In FIG. 19, reference numeral 116 represents a surface area of acondensing heat transmission portion, and 117 represents a surface areaof a heat transmission portion of the condensed water. The surface areas116 and 117 of the heat transmission portions and the liquid levelposition 112 have the following relationship.

The conventional Rankine cycle apparatus 100 inherently has thecharacteristic that the liquid fluid position 112 varies. Namely,because the engine output varies in response to traveling start/stop andtransient traveling velocity variation of the vehicle, the amount ofwater supply to the evaporator 111 also varies, in response to which theliquid level position 112 within the condenser 100 varies. Namely, inthe condenser 100, the liquid level position 112 rises when the amountof the vapor flowing into the condenser 100 (i.e., inflow amount of thevapor) is greater than the amount of the condensed water discharged fromthe condenser 100 (i.e., discharge amount of the condensed water), butlowers when the inflow amount of the vapor is smaller than the dischargeamount of the condensed water. In this way, the vapor-occupied portion(104) in the cooling pipes 103 of the condenser 100 increases ordecreases. Because the condensed water (in the portion 105) isdischarged from the water supplying pump unit 110 subjected topredetermined flow rate control, a pressure from an outlet port 113 ofthe expander 107 to an inlet port 114 of the water supplying pump unit110 is determined by a pressure within the condenser 100. The pressurewithin the condenser 100 is determined by an amount of condensing heatexchange caused by cooling of the vapor portion of the condenser, andthe amount of condensing heat exchange is determined by a flow rate ofthe medium to be cooled and a surface area of the condensing heattransmission portion 116. Thus, if the portion occupied with the vaporincreases or decreases due to variation (rise or fall) of the liquidlevel position 112, the surface area 116 of the condensing heattransmission portion increases or decreases and so the pressure withinthe condenser 100 and the flow rate of the medium to be cooled do notuniformly correspond to each other any longer.

Similarly, the temperature of the condensed water at the outlet port ofthe condenser 100 is determined by an amount of heat exchange caused bycooling of the water portion (105) of the condenser, and the amount ofthe heat exchange of the condensed water is determined by the flow rateof the medium to be cooled and a surface area 117 of a heat transmissionportion of the condensed water. Thus, if the portion occupied with thecondensed water (105) increases or decreases due to variation (rise orfall) of the liquid level position 112, the surface area 117 of the heattransmission of the condensed water portion increases or decreases andso the temperature of the condensed water and the flow rate of themedium to be cooled do not uniformly correspond to each other anylonger. When the high-temperature vapor has reached an unusually highpressure due to some system anomaly in the above-described Rankine cycleapparatus, there arises a need to promptly restore the vapor from theunusually high pressure to a normal pressure without hindering thefunctions of relevant components.

For that purpose, a chlorofluorocarbon-turbine composite enginedisclosed in Japanese Patent Laid-Open Publication No. SHO-49-92439includes a pressure relief valve provided in a branch vapor pipe.Namely, in this composite engine, the outlet of an evaporator and theinlet of a condenser are connected by the branch vapor pipe via therelief valve, so that vapor can be bypassed when the interior pressureof the evaporator is at high level. However, with this composite engine,which is constructed to only adjust the pressure via the pressure reliefvalve provided in the branch vapor pipe, it is difficult toappropriately control a high-pressure vapor in and near the evaporator.

Further, Japanese Utility Model Laid-Open Publication No. SHO-58-124603discloses a Rankine cycle apparatus which includes control valvesbetween a condenser and a liquid tank and near the outlet of anevaporator. The control valves function to close circulation circuitrywhile the apparatus is in an OFF state or in a non-operating state, soas to prevent a liquid-phase working medium from filling an expander andcondenser. With these control valves, however, the disclosed Rankinecycle apparatus can not quickly respond to a pressure increase between awater supplying pump and the evaporator.

Generally, when a high pressure, exceeding an allowable maximum pressurelevel of the expander or evaporator, has been produced within thecirculation circuitry of the Rankine cycle apparatus, for example, dueto a stagnated flow of the working medium, there arises a need todischarge the high-temperature and high-pressure working medium out ofthe circulation circuitry in order to promptly lower the pressure sothat the expander, evaporator, etc. can be properly protected and canreadily resume their operations. In such a case, it is necessary tolower the temperature and pressure of the working medium itself andminimize adverse influences exerted by the working medium on peripheraldevices, such as an exhaust device of a vehicle engine.

Further, it is necessary to lower the pressure in quick response to ahigh-pressure vapor in and near the evaporator and a rapid pressureincrease, beyond the allowable maximum pressure level, of water betweenthe pump and the evaporator.

SUMMARY OF THE INVENTION

The present invention provides an improved Rankine cycle apparatusconstructed into a closed circulation circuit, which comprises: anevaporator for heating and thereby converting a liquid-phase workingmedium into a gaseous-phase working medium, using heat from a heatsource; an expander for converting heat energy of the gaseous-phaseworking medium, discharged by the evaporator, into mechanical energy; acondenser for cooling and thereby converting the gaseous-phase workingmedium, discharged by the expander, to the liquid phase; a supply pumpfor supplying, in a pressurized condition, the liquid-phase workingmedium, discharged by the condenser, to the evaporator, and a dischargevalve device provided between the supply pump and the evaporator in aportion of the closed circulation circuit where the working medium ispresent in a liquid-phase state. When the interior pressure of theclosed circulation circuit is higher than a predetermined limit pressurelevel that is lower than at least an allowable maximum pressure level ofthe expander or the evaporator, the discharge valve device dischargesthe working medium out of the closed circulation circuit.

When the flow of the working medium stagnates in the expander orevaporator, a high pressure, exceeding the allowable maximum pressurelevel of the expander or evaporator, is produced within the closedcirculation circuit. In such a case, the water-phase working medium isfirst discharged via a relief valve of the valve device out of thecirculation circuit. Then, the gaseous-phase working medium (saturatedvapor), having been lowered in temperature and pressure is alsodischarged via the relief valve out of the circulation circuit. In thisway, the pressure within the expander or evaporator in the closedcirculation circuit can be reliably prevented from exceeding theallowable maximum pressure level; thus, the evaporator and expander canbe reliably protected from excessive pressure, and the operations of thecomponents can be readily resumed. Further, because the working mediumitself is lowered in temperature and pressure as the high-pressure andhigh-temperature working medium is discharged out of the closedcirculation circuit, the present invention can minimize adverseinfluences exerted by the working medium on peripheral devices, such asan exhaust device of an engine. Furthermore, the present invention canlower the pressure in quick response to a high-pressure vapor in andnear the evaporator and a rapid pressure increase, beyond the allowablemaximum pressure level, of water present in a pipe between the supplypump and the evaporator.

Preferably, in the present invention, at least a portion of the workingmedium to be discharged out of the closed circulation circuit via thedischarge valve device is discharged around the heat source. Therefore,the heat source of the evaporator and the evaporator itself can becooled with the discharged working medium; particularly, appropriatepressure reduction can be achieved by lowering the temperature of thegaseous-phase working medium. Further, the present invention canminimize adverse influences on the peripheral devices and can preventexcessive heating due to excessive temperature increase of the heatsource (e.g., exhaust passageway of the engine) and evaporator.

Preferably, in the present invention, the discharge valve deviceincludes a plurality of discharge passageways for directing the workingmedium out of the closed circulation circuit, and a flow rate limiter,such as an orifice, is provided in at least one of the plurality ofdischarge passageways. With the flow rate limiter capable of adjustingthe discharge flow rate of the working medium, it is possible to adjustthe adverse influences on the peripheral devices. Particularly, thepresent invention can achieve an optimal discharge flow rate toappropriately prevent rapid cooling of, and hence thermal impact on, thehigh-temperature heat source (e.g., exhaust passage-way of the engine)and other components peripheral to the heat source and the evaporator.In this way, the present invention permits appropriate cooling of thecomponents.

Further, the discharge valve device is preferably disposed at leastcloser to the pump unit than the evaporator. Thus, the discharge valvedevice is located remote from the evaporator, so that the amount of theliquid-phase working medium discharged, via the discharge valve device,out of the closed circulation circuit can be increased accordingly.Also, the discharge of the liquid-phase working medium can lower thetemperature and pressure within the circulation circuit, which canreduce the pressure of the gaseous-phase working medium to besubsequently discharged out of the closed circulation circuit andthereby lower the discharge pressure (flow rate) of the gaseous-phaseworking medium. As a result, adverse influences on the peripheraldevices can be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain preferred embodiments of the present invention will hereinafterbe described in detail, by way of example only, with reference to theaccompanying drawings, in which:

FIG. 1 is a block diagram showing a general system setup of a Rankinecycle apparatus in accordance with an embodiment of the presentinvention;

FIG. 2 is a sectional view illustrating an inner structure of a watersupplying pump unit of FIG. 1;

FIG. 3 is a view of example layout of various components of the Rankinecycle apparatus of FIG. 1 when mounted on a vehicle;

FIG. 4 is a graph showing variation over time of exhaust gas energy;

FIG. 5 is a graph showing variation over time of a target amount ofwater supply;

FIG. 6 is a graph showing variation over time of a vapor pressure;

FIG. 7 is a vertical sectional view showing a specific example of asecond relief valve in the Rankine cycle apparatus;

FIG. 8 is a partly-sectional view showing a specific example of a firstrelief valve in the Rankine cycle apparatus, which is of a rupture-type;

FIGS. 9A and 9B are perspective views of a rupture disk of therupture-type relief valve shown in FIG. 8;

FIG. 10 is a block diagram showing a system setup of the Rankine cycleapparatus, which particularly shows flows of a working medium in theapparatus;

FIG. 11 is a side view showing an inner structure of a condenser andother components peripheral to the condenser in the Rankine cycleapparatus of FIG. 1;

FIG. 12 is a sectional view showing a structure of an air vent in itsclosed position;

FIG. 13 is a sectional view of the air vent taken along the A-A lines ofFIG. 12;

FIG. 14 is a sectional view of the air vent in an opened position;

FIG. 15 is a graph showing respective saturation curves of atemperature-sensitive liquid and water;

FIGS. 16A and 16B are a view and table explanatory of details of liquidlevel position settings;

FIG. 17 is a flow chart showing an operational sequence of liquid levelposition control;

FIG. 18 is a timing chart showing variation in a traveling velocity ofthe vehicle having the Rankine cycle apparatus mounted thereon,variation in an engine output, variation in an amount of water supply toan evaporator and variation in the liquid level position within thecondenser; and

FIG. 19 is a schematic view of a conventional vehicle-mounted Rankinecycle apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a description will be made about an example general setup of aRankine cycle apparatus in accordance with an embodiment of the presentinvention, with reference to FIG. 1.

The Rankine cycle apparatus 10 includes an evaporator 11, an expander12, a condenser 13, and a water supplying pump unit 14 provided with asupply pump.

The evaporator 11 and the expander 12 are interconnected via a pipe 15,and the expander 12 and the condenser 13 are interconnected via a pipe16. Further, the condenser 13 and the water supplying pump unit 14 areinterconnected via a pipe 17, and the water supplying pump unit 14 andthe evaporator 11 are interconnected via a pipe 18. With such a pipingstructure, there is formed closed circulation circuitry (circulationsystem) through which a working medium is circulated within the Rankinecycle apparatus 10 in the gaseous or liquid phase. The working medium inthe Rankine cycle apparatus 10 is in water (liquid) and water vapor(gaseous) phases.

The circulation circuitry of the Rankine cycle apparatus 10 has acirculating structure hermetically sealed from the outside, which allowswater or vapor to circulate therethrough.

In the circulation circuitry of the Rankine cycle apparatus 10, thewater (liquid-phase working medium) travels from a liquid levelposition, indicated by a broken line P1, within the condenser 13,through the water supplying pump unit 14, to the evaporator 11. In FIG.1, the pipes 17 and 18, through which the water travels, are indicatedby thick solid lines. The vapor (gaseous-phase working medium) travelsfrom the evaporator 11, through the expander 12, to the liquid levelposition P1 within the condenser 13. The pipes 15 and 16, through whichthe vapor travels, are indicated by thick broken lines.

The pipe 18, extending in a low temperature region between the watersupplying pump unit 14 and the evaporator 11, has two branch pipes 200and 201. First and second relief valves 22 and 202 are provided in thebranch pipes 200 and 201, respectively.

Discharge (relief) valve device 203 is provided, in a portion of thecirculation circuitry, for discharging the liquid-phase working mediumout of the circulation circuitry when the circuitry has an interiorpressure higher than a predetermined upper limit pressure. At least aportion of the working medium discharged out of the closed circuitry viathe discharge valve device 203 is discharged around an exhaust pipe 45that functions as a heat source of the Rankine cycle apparatus 10.

The discharge valve device 203 includes a plurality of dischargepassageways (discharge pipes) 204, 205, 206, 207 and 208 for dischargingthe working medium out of the closed circuitry. Flow rate limiter (suchas an orifice) 209 is provided in at least one of the dischargepassageways. The discharge valve device 203 is disposed closer to thewater supplying pump unit 14 than the evaporator 11.

Note that, although the embodiment of FIG. 1 is shown as including two,i.e. first and second, relief valves 22 and 202, it may include only onesuch relief valve.

The Rankine cycle apparatus 10 is constructed to phase-convert waterinto water vapor using heat from the heat source, and produce mechanicalwork using expansion of the water vapor. The evaporator 11 is amechanism for converting water into vapor.

As will be later described in detail, the Rankine cycle apparatus 10 isconstructed as a vehicle-mounted apparatus suitable for mounting on anautomotive vehicle. For that purpose, the evaporator 11 uses heat ofexhaust gas from the vehicle engine as the heat source. Namely, theevaporator 11 uses heat of the exhaust gas, flowing through an exhaustpipe 45 of the engine (internal combustion engine), to heat andsuperheat water supplied from the water supplying pump unit 14, so as toproduce high-temperature and high-pressure water vapor. Thehigh-temperature and high-pressure water vapor produced by theevaporator 11 is supplied to the expander 12.

Needless to say, the evaporator 11 may use higher-temperature exhaustgas from an exhaust port, exhaust manifold (not shown) or the likelocated downstream of an exhaust valve of the engine, rather than fromthe exhaust pipe 45.

The expander 12 has an output shaft 12 a connected to the rotor (notshown) or the like of a motor/generator (M/G) 19 so as to allow themotor/generator (M/G) 19 to operate as a generator. The expander 12 isconstructed to expand the high-temperature and high-pressure water vaporsupplied from the evaporator 11 and rotates the output shaft 12 athrough the expansion of the vapor. The rotation of the output shaft 12a rotates the rotor of the motor/generator 19 to cause themotor/generator 19 to make predetermined mechanical rotation or performpredetermined power generation operation. The output shaft 12 a of theexpander 12 is also connected to a hydraulic pump 25 to drive the pump25.

As noted above, the expander 12 produces mechanical work through theexpansion of the high-temperature and high-pressure water vapor suppliedfrom the evaporator 11 via the pipe 15 and thereby drives various loads,such as the motor/generator 19 and hydraulic pump 25. The vapor 12discharged from the evaporator 12 decreases in temperature and pressureand is delivered via the pipe 16 to the condenser 13 with the decreasedtemperature and pressure.

The condenser 13 cools and liquefies the vapor delivered from theevaporator 12. Water produced through the liquefaction by the condenser13 (i.e., condensed water) is returned via the pipe 17 to the watersupplying pump unit 14.

High-pressure pump 44 of the water supplying pump unit 14 pressurizesthe water liquefied by the condenser 13 i.e., condensed water from thecondenser 13) and re-supplies or replenishes the pressurized condensedwater to the evaporator 11.

The Rankine cycle apparatus 10 having the above-described general systemsetup includes the following as other relevant components.

Within a casing 21 of the expander 12, there is provided a breather(separator) 23 for returning leaked water vapor to the pipe 16. Further,within the casing 21, an oil pan 24 is disposed under the expander 12.Oil built up in the oil pan 24 with water mixed therein is delivered bythe hydraulic pump 25 to an oil coalescer 27 via a pipe 26.

The oil and water are separated from each other by the oil coalescer 27,and the separated water is stored in a lower portion of an oil tank 28due to a difference in specific gravity. Valve mechanism 30 operating onthe basis of a float sensor 29 is mounted in the oil tank 28.

The oil separated from the water by the oil coalescer 27 and stored inan upper portion of the oil tank 28 is supplied, through a pipe 31, tovarious sections of the expander 12 by way of an oil path (not shown)formed in the output shaft 12 a.

The water stored or accumulated in the lower portion of the oil tank 28is supplied, via a pipe 33, to an open tank 32 of the water supplyingpump unit 14 through operation of the valve mechanism 30. The open tank32 is so named because it is open to the atmospheric air, and itaccumulates or stores therein the working medium, leaked or dischargedout of the circulation circuitry, in the liquid-phase state.

The open tank 32 of the water supplying pump unit 14 and the condenser13 are interconnected by a pipe 35 via a water supplying return pump 37and check valve 34.

The condenser 13 includes a liquid level sensor 38 and air vent 39provided near the liquid level position. Water supply from the open tank32 to the condenser 13 is performed by the water supplying return pump37 that is driven by a motor 36 turned on/off in response to a signalfrom the liquid level sensor 38. Further, the open tank 32 and thecondenser 13 are interconnected by a pipe 40 that discharges the watervia the air vent 39.

The pipe 17 for returning the condensed water discharged from thecondenser 13 is connected to a water coalescer 42 within a sealed tank41 of the pump unit 14. Water in the sealed tank 41 is supplied, by thehigh-pressure water supplying pump 44 driven by a motor 43, to theevaporator 11 via the pipe 18.

Further, in association with the condenser 13, there are provided aplurality of cooling fans 46-48 for generating cooling air independentlyfor different portions of the condenser 13.

In the above-described arrangements, a working medium supply device isconstituted by elements pertaining to the liquid level position withinthe condenser 13 and lower section of the condenser 13 and by the watersupplying pump unit 14.

In the closed working medium circulation system of the Rankine cycleapparatus 10, a working medium leaked from the breather 23 of theexpander 12 is returned via an outlet port P2 to the pipe 16 of thecirculation system.

FIG. 2 is a view showing an example specific structure of the watersupplying pump unit 14.

The water supplying pump unit 14 comprises the water coalescer 42,sealed tank 41, high-pressure water supplying pump 44 driven by thedrive motor 43, open tank 32, return pump 37, and check valve 34.

Although a rotation shaft 49 of the drive motor 43 is shown in thefigure as being parallel to the surface of the sheet of the drawing,this is just for convenience of illustration; in practice, the rotationshaft 49 is disposed perpendicularly to the sheet of the drawing. Therotation shaft 49 of the drive motor 43 is held in engagement with a cammechanism 49 a, so as to function as a cam shaft.

The water coalescer 42 separates oil and water, and the sealed tank 41directly collects leaked water from the high-pressure water supplyingpump 44. The high-pressure water supplying pump 44 supplies a requiredamount of water by performing water amount control based on the numberof pump rotations.

The open tank 32 is provided for temporarily storing water leaked out ofthe circulation circuitry. The return pump 37 returns the leaked waterto the sealed tank 41 or to a supercooler of the condenser 13. Namely,the return pump 37 returns the leaked water from the open tank 32 to theclosed tank 41 through a pipe 152 equipped with a check valve 151, ordelivers the water to the supercooler of the condenser 13 through thepipe 35 equipped with the check valve 34 as necessary. The check valve151 of the pipe 152 prevents a reverse flow of the water from the sealedtank 41, and the check valve 34 of the pipe 35 prevents a reverse flowof the water from the supercooler of the condenser 13.

Water discharged from the outlet port 13 a (see FIG. 1) of the condenser13 is passed through the water coalescer 42 via the pipe 17 so that thewater is separated from oil and only the water is fed to thehigh-pressure water supplying pump 44 driven by the drive motor 43. Thehigh-pressure water supplying pump 44 delivers the water to theevaporator 11 via the pipe 18. Leaked water is returned via the pipe 40to the open tank 32.

Now, a description will be made about the discharge device 203, withreference to FIG. 1.

In the discharge device 203, the first relief valve 22 is positionedbetween the outlet of the high-pressure water supplying pump 44 and theinlet of the evaporator 11. The first relief valve 22 causes the workingmedium to be discharged in the water-phase state to reduce the interiorpressure and then causes the vapor, having flown backward from theevaporator 11, to be discharged (relieved) in low pressure condition.Two relief circuits are provided to extend from the first relief valve22 to the evaporator 11. The first relief circuit comprises the pipe 204for discharging the working medium into the exhaust pipe 45 extendingfrom the downstream end of the evaporator 11, while the second reliefcircuit comprises the pipe 205 for discharging the working medium intothe exhaust pipe 45 extending from the upstream end of the evaporator11.

When the first relief valve 22 has been activated, the system has to bedeactivated promptly. As noted above, the first relief valve 22 causesthe working medium to be discharged in the water-phase state, during aninitial stage of high-pressure condition, to thereby reduce the interiorpressure and then causes the vapor, having flown backward from theevaporator 11, to be discharged (relieved). Therefore, the branch pipe200 associated with the first relief valve 22 should not be positionedvery close to the evaporator 11; namely, it is preferable that thebranch pipe 200 be close to the outlet of the high-pressure watersupplying pump 44 and as close to the exhaust pipe 45 as possible.

When the first relief valve 22 has been activated, flows of the waterand vapor within heat transmission pipes of the evaporator 11 stop atonce, and then stat flowing back toward the pipe 18. Therefore, if theheat flow amount of the exhaust gas is great, then the temperature ofthe heat transmission pipes is likely to increase excessively.Therefore, for the discharge, via the first relief valve 22, of thewater or the vapor, there are provided two discharge (relief)destinations via the first relief circuit (pipe 204); and the secondrelief circuit (pipe 205). The following paragraphs explain respectivestructural features of the first and relief circuits that function whenthe temperature of the heat transmission pipes has increasedexcessively.

(1) First Relief Circuit (Pipe 204):

Where the water etc. is discharged to the downstream exhaust pipe 45 ofthe evaporator 11, there is no need to provide the flow rate adjustmentmechanism, such as an orifice, in the pipe 204, and thus thewater-circulating circuit can be implemented using a simplest structure.Consequently, the first relief circuit can lower the pressure of thehigh-pressure circuit more quickly than the second relief circuit.However, when the first relief valve 22 has been activated in the firstrelief circuit during operation with a high heat load, the evaporator 11would temporarily perform its heating operation without water, so thatsecondary damages to the heat transmission pipes might be caused due toan excessive temperature increase. Thus, there is a need to prevent anexcessive heat amount from being transferred to the evaporator 11, e.g.by performing control for rapidly limiting the engine outputsimultaneously with activation of the first relief valve 22.

(2) Second Relief Circuit (Pipe 205):

Where the water etc. is discharged to the upstream exhaust pipe 45 ofthe evaporator, on the other hand, a large amount of the working mediumcan be emitted instantaneously toward the evaporator 11 because thedestination of the working medium discharge by the relief circuit is theupstream side of the evaporator 11.

However, if the emission amount of the working medium is excessive, theheat transmission pipes and casing member of the evaporator 11 may becooled so rapidly as to undesirably invite a possibility ofdeterioration of the components due to thermal impact. Thus, in theinstant embodiment, the orifice 209 is provided in the pipe 205 toachieve an optimal emission amount of the working medium correspondingto the heat capacity of the evaporator 11. In this way, the instantembodiment can effectively avoid rapid cooling of the heat transmissionpipes and secondary damages to the heat transmission pipes due to theexcessive temperature increase although the pressure lowering speed ofthe high-pressure circuit may be slightly sacrificed, so that the engineoutput can be lowered progressively.

Further, the cooling by the second relief circuit cools the heat source(exhaust pipe 45) producing high-temperature and high-pressure vapor inthe evaporator 11 and the thus-produced high-temperature andhigh-pressure vapor as well, and thus the vapor-phase working medium tobe discharged can be further reduced in temperature and pressure.

The following paragraphs describe the Rankin cycle apparatus 10 whenmounted on the vehicle, with reference to FIG. 3.

In FIG. 3, reference numeral 301 indicates a front body of the vehicle,and 302 a front road wheel. Engine room 303 is formed within the frontbody 301, and the engine 50 is mounted in the engine room 303. Theexhaust manifold 51 is provided on a rear surface portion of the engine50, and the above-mentioned exhaust pipe 45 is connected to the exhaustmanifold 51.

The evaporator 11 is mounted on a portion of the exhaust pipe 45 nearthe exhaust manifold 51. The pipe 18 extending from the high-pressurewater supplying pump 44 is coupled to the evaporator 11, and the pipe 18supplies water to the evaporator 11 using, as its heat source, the heatof exhaust gas from the high-pressure water supplying pump 44. Theevaporator 11 phase-converts the water into water vapor using the heatof the exhaust gas and supplies the converted vapor to the expander 12via the pipe 15 connected to a vapor inlet port 52 of the expander 12.The expander 12 converts expansion energy of the water vapor intomechanical energy.

The expander 12 has a vapor outlet port 53 connected to the pipe 16, andthe condenser 13 for cooling/condensing water vapor into water isdisposed between the pipe 16 and the sealed tank 41 leading to an inletside of the high-pressure water supplying pump 44. The condenser 13 islocated in a front area of the engine room 203. In FIG. 3, there is alsoshown a layout of the open tank 32, water coalescer 42, return pump 37,oil coalescer 27, super cooler 54 (liquid-phase portion of the condenser13), air vent 39, check valve 34, etc. The high-pressure water supplyingpump 44, evaporator 11, expander 12, condenser 13, etc. togetherconstitute the Rankine cycle apparatus for converting heat energy intomechanical energy, as noted above.

Behavior of the Rankine cycle apparatus is explained below in the orderthat corresponds to the flows of water and water vapor within theRankine cycle apparatus.

Water cooled and condensed in the condenser 13 is supplied, in apressurized condition, by the high-pressure water supplying pump 44 tothe evaporator 11 via the pipe 18.

The water, which is a liquid-phase working medium, is heated by theevaporator 11 imparting the water with heat energy until it becomeshigh-temperature and high-pressure water vapor, and the resultanthigh-temperature and high-pressure water vapor is supplied to theexpander 12. The expander 12 converts the heat energy into mechanicalenergy through expanding action of the high-temperature andhigh-pressure water vapor, and the mechanical energy is supplied to themotor/generator 19 annexed to the expander 12.

The water vapor let out from the expander 12 assumes a loweredtemperature and pressure, which is then delivered to the condenser 13.The water vapor of lowered temperature and pressure delivered to thecondenser 13 is again cooled and condensed in the condenser 13, and theresultant condensed water is supplied via the water coalescer 42 to thehigh-pressure water supplying pump 44. After that, the water, which is aliquid-phase working medium, repeats the above circulation, so that theexpander 12 continues to be supplied with water vapor of hightemperature and pressure.

Next, a description will be made about settings of respective workingpressures of the first and second relief valves 22 and 202 of thedischarge valve device 203, with reference to FIGS. 4-6. FIG. 4 is agraph showing variation over time in exhaust gas energy, FIG. 5 is agraph showing variation over time in target water supply amount, andFIG. 6 is a graph showing variation over time in vapor pressure.

The exhaust gas energy varies as illustrated in FIG. 4 in response tostart and stop operations of the vehicle. The vapor pressure varies asdepicted by curves P1, P2 and P3 of FIG. 6 in response to variation inthe exhaust gas energy and target water supply amount of FIG. 5.Straight line L10 of FIG. 6 represents an allowable maximum pressurelevel of the expander or evaporator. Thus, the working pressures of therelief valves are set to be higher than a normal working pressure C13,as represented by a first limit working pressure (straight line C11) andsecond limit working pressure (straight line C12).

Where only the second relief valve 202 is used solely, its workingpressure is set to the first limit working pressure C11 that is abouttwice as great as the normal system working pressure C13 of the Rankinecycle apparatus 10. Thus, the second relief valve 202 functions toreduce only an excessive pressure while maintaining the system workingpressure, so that the appropriate operation of the Rankine cycleapparatus 10 can be maintained reliably. Relief circuit associated withthe second relief valve 202 is constructed by connecting the reliefvalve 202 to the exhaust pipe 45 via the pipe 207 as shown in FIG. 1,and by connecting the relief valve 202 to the open tank 32 via the pipe208 so that the working medium can be recovered for recycling.

Where only the first relief valve 22 is used solely, its workingpressure is set to the second limit working pressure C12 that is abouttwice and half as great as the normal system working pressure C13 of theRankine cycle apparatus 10. Thus, the first relief valve 22 reliablyperforms the pressure release operation at or below an allowable maximumpressure level close to upper pressure level limits of the evaporatorand expander, so that the evaporator and expander can be reliablyprotected from excessive pressure; the operations of these componentscan be readily resumed after replacement of a rupture disk of the firstrelief valve 22.

Further, where the first and second relief valves 22 and 202 are used incombination, each of these relief valves 22 and 202 is set to the sameworking pressure as in the case where it is used solely as mentionedabove. In this way, fail-safe protection can be achieved againsterroneous operation or malfunction of each of the relief valves 22 and202.

FIG. 7 is a vertical sectional view of the second relief valve 202,which includes a valve body 401, a valve support 402 screwed to thevalve body 401, and a cap 403 screwed to the valve support 402. Axialvalve member 406 is vertically-movably supported via an O-ring 404 andsealing member 405 and normally resiliently urged by a spring 407disposed in an upper portion of the second relief valve 202. Once apressure externally applied to the interior of a pipe opening 408exceeds a reference value preset for the second relief valve 202, theapplied pressure causes the axial valve member 406 to press at its upperend the spring 407 so that a gap is formed, between the O-ring 404 andthe axial valve member 406, to permit leakage through the gap

FIG. 8 is a partly-sectional view of one embodiment of the first reliefvalve 22 which is constructed as a rupture-type relief valve. The firstrelief valve 22 includes a first holder 410, a second holder 411, and arupture disk 413 supported by a back-up ring 412 within the first holder410.

As shown in FIGS. 9A and 9B, the rupture disk 413 has a central diskportion 414 that opens to permit leakage therethrough when a pressuregreater than a predetermined level is applied thereto (FIG. 9B).

Next, a description will be made about control of the liquid levelposition of water accumulated in the condenser 13 of the Rankine cycleapparatus 10, with reference to FIGS. 10-18.

FIG. 10 shows the system of the Rankine cycle apparatus 10 with acentral focus on the condenser 13, which particularly shows a front viewof the condenser 13 as taken from before the vehicle; more specifically,states of the working medium (water or condensed water W1 and watervapor W2) within the condenser 13 are illustrated. FIG. 11 is a sideview of the cooling device condenser 13, which shows positionalrelationship among cooling fans 46, 47 and 48 provided for the condenser13 as well as inner states of the condenser 13.

The condenser 13 includes a vapor introducing chamber 13A in its upperend portion, a water collecting chamber 13B in its lower end portion,and an intermediate chamber 56. A plurality of cooling pipes 55 areprovided between the vapor introducing chamber 13A and the intermediatechamber 56 and between the intermediate chamber 56 and the watercollecting chamber 13B, and these three chambers 13A, 13B and 56 are influid communication with each other. Cooling fins 55 a are provided onthe outer periphery of the cooling pipes 55.

The vapor introducing chamber 13A of the condenser 13 is connected viathe pipe 16 to the vapor outlet port 53 of the expander 12, and thewater collecting chamber 13B is connected via the pipe 17 to the watersupplying pump unit 14. As noted earlier, the expander 12 is connectedvia the pipe 15 to the evaporator 11, and the water supplying pump unit14 is connected via the pipe 18 to the evaporator 11.

The evaporator 11 receives heat 50A from the exhaust gas of the engine(heat source) 50 via the exhaust pipe 45 (see FIG. 1). Within the watersupplying pump unit 14, there are included various components, such asthe sealed tank 41, water coalescer 42, high-pressure water supplyingpump 44, drive motor 43, open tank 32, return pump 37 and motor 36.

In the condenser 13, water vapor W2 is cooled and condensed to turn towater (condensed water) W1 and accumulated in a lower inner portion ofthe condenser 13. Horizontal line drawn in the figure within theintermediate chamber 56 represents a liquid level 65 (corresponding tothe liquid level position P1 of FIG. 1) that indicates a liquid levelposition of the water W1 accumulated in the condenser 13.

The liquid level sensor 38 and intermediate discharge port 59 areprovided at a position corresponding to the position of the liquid level65. The liquid level sensor 38 outputs a detection signal,representative of the liquid level position detected thereby, to acontrol device 60. The control device 60 generates a motor controlinstruction signal on the basis of the liquid level position detectionsignal from the sensor 38 and sends the motor control instruction signalto the motor 36 of the return pump 37.

The air vent 39 for water vapor is coupled to the intermediate dischargeport 59, and it has an output end communicating with the open tank 32via the pipe 40 equipped with a check valve 58. Exhaust pump 57 isannexed to the pipe 40 in parallel relation thereto.

Further, as seen in FIG. 11, the cooling fan 46 is disposed adjacent therear surface (right side surface in the figure) of the condenser 13 incorresponding relation to a gaseous-phase portion or vapor condensingportion 70 of the condenser 13 where the vapor W2 is accumulated, andthe cooling fans 47 and 48 are disposed adjacent the rear surface of thecondenser 13 in corresponding relation to a liquid-phase portion orcondensed water cooling portion 71 of the condenser where the water W1is accumulated.

The cooling operation by the cooling fan 46 is controlled by a pressurecontrol device 62 on the basis of a vapor pressure detection signaloutput by a pressure sensor 61 mounted, for example, on the pipe 16through which the vapor W2 flows. Namely, the cooling fan 46 is avapor-condensing cooling fan to be used for vapor pressure adjustment.Further, the cooling operations by the cooling fans 47 and 48 arecontrolled by a temperature control device 64 on the basis of a watertemperature detection signal output by a temperature sensor 63 mounted,for example, on the pipe 17 through which the water W1 flows. Namely,the cooling fans 47 and 48 are water-cooling fans to be used for coolingof the condensed water.

In FIG. 11, A1 indicates a flow of cooling air applied from before thegaseous-phase portion 70 of the condenser 13 on the basis of therotation of the cooling fan 46, while A2 indicates a flow of cooling airapplied from before the liquid-phase portion 71 of the condenser 13 onthe basis of the rotation of the cooling fans 47 and 48.

As apparent from the foregoing, the gaseous-phase portion or vaporcondensing portion 70 and the liquid-phase portion or condensed watercooling portion 71 in the condenser 13 are cooled independently of eachother. Reference numeral 72 represents shrouds that zone or define theindividual cooling regions.

Referring back to FIG. 10, the water vapor discharged from the vaporoutlet port 53 of the expander 12 is substantially equivalent inpressure to the atmospheric pressure. In the intermediate chamber 56into which the respective outlets of the upper cooling pipes (condensingpipes) 55 open, water is discharged via the air vent 39 in order toadjust the liquid level 65 to lie within the intermediate chamber 56.Further, the high-pressure water supplying pump 44 functions, as a watersupplying pump of a main circulation circuit in the Rankine cycleapparatus 10, to supply a necessary amount of water to the evaporator11.

The reserving open tank 32, which is open to the atmospheric air,retains reserve water for the sealed circulation circuitry in thesystem. The return pump 37 supplies water into the condenser 13 inresponse to the detection signal from the liquid level sensor 38. Theexhaust pump 57 sucks in air from the downstream end of the air vent 39when the condenser 13 is to be operated at a negative pressure.

The above-mentioned exhaust pump 57 may be constructed to operate inresponse to detection of a negative pressure by the pressure sensor 61and pressure control device 62 shown in FIG. 11, or by the controldevice 60 detecting via the liquid level sensor 38 when the position ofthe liquid level 65 rises above a predetermined upper limit.

The check valve 58 prevents a reverse flow of the atmospheric air whenthe interior pressure of the condenser 13 turns to a negative pressure,and the check valve 34 prevents a reverse flow of water from thecondenser 13 to the return pump 37. The air vent 39 is constructed toallow water and air to pass therethrough, but prevent water vapor frompassing therethrough. The intermediate discharge port 59 functions tolimit variation in the position of the liquid level 65 of the condensedwater, through emission of non-condensing gas or overflow of the water,so that the liquid level position varies only within a predeterminedvertical range.

The liquid sensor 38 outputs a position detection signal, representativeof an actual current position of the liquid level 65, to the controldevice 60, and the control device 60 controls the return pump 37 so thatthe position of the liquid level 65 constantly lies within theintermediate chamber 56. More specifically, the position of the liquidlevel 65 is controlled to lie within a predetermined vertical rangebetween the air vent 39 and the liquid level sensor 38. The liquid levelsensor 38 may be, for example, in the form of a capacitance-type levelsensor or float-type level switch.

In FIG. 11, the pressure sensor 61 detects an interior pressure of thecondenser 13; basically, it detects a pressure of the water vapor W2.The pressure control device 62 operates the cooling fan 46 in such amanner that the interior pressure of the condenser 13 equals apredetermined pressure setting. The temperature sensor 63 detects acurrent temperature of the condensed water W1. The temperature controldevice 64 operates the cooling fans 47 and 48 in such a manner that thecondensed water temperature equals a predetermined temperature setting.

Next, construction and behavior of the air vent 39 employed in theinstant embodiment will be detailed with reference to FIGS. 12 to 14.FIG. 12 is a vertical sectional view of the air vent 39 and FIG. 13 is asectional view of the air vent 39 taken along the A-A lines of FIG. 12,both of which show the air vent 39 in a closed position. FIG. 14 is avertical sectional view of the air vent 39 in an opened position(valve-open position). In FIG. 12, the left side of the air vent 39 is aside communicating with the condenser 13 (i.e., “condenser side”), whilethe right side of the air vent 39 is a side communicating with theatmosphere (i.e., “atmospheric air side”). The air vent 39 ishermetically sealed when its interior is filled with saturated vapor(FIG. 12), automatically opened when water or non-condensing gas ispresent in the interior, and again hermetically sealed by dischargingthe water or non-condensing gas (FIG. 14).

In FIG. 12, the air vent 39 includes a valve 66 located generallycentrally therein, a valve support 67 supporting the valve 66, and avalve port (packing) 68.

The valve 66 supported by the valve support 67 is positioned to close upthe valve port 68 when necessary. The valve 66 comprises a pair ofopposed diaphragms 66 a combined to form a hermetically-sealed spacetherebetween, and temperature-sensitive liquid 69 is held in the sealedspace. The temperature-sensitive liquid 69 has characteristics suchthat, like water, it is kept in the liquid phase under less than apredetermined pressure or temperature but expands as a gas once thetemperature exceeds a predetermined level.

FIG. 15 shows respective saturation curves C1 and C2 of thetemperature-sensitive liquid 69 and water. The temperature at which thetemperature-sensitive liquid 69 turns to the gaseous state is lower byAT (about 10° C.) than the temperature at which water turns to watervapor. Thus, when the interior of the air vent 39 is filled with thewater vapor W2, the temperature-sensitive liquid 69 is kept in thegaseous state, so that the sealed space containing the expandedtemperature-sensitive liquid 69 presses the opposed diaphragms 66 aoutwardly away from each other so as to close up a gap between the valveport 68 and the valve 66 comprised of the diaphragms 66 a (see FIG. 12).Conversely, when the interior of the air vent 39 is at a low temperature(e.g., when non-condensing gas A3, such as air, is present in theambient environment around the valve 66), the temperature-sensitiveliquid 69 is kept in the liquid state, the opposed diaphragms 66 a arepressed inwardly toward each other, so that air etc. is dischargedthrough the gap between the valve 66 and the valve port 68 (see FIG.14).

As apparent from the foregoing, the control device 60 shown in FIG. 10is constructed to control the position of the liquid level 65 to varyonly within the predetermined vertical range (variation width) in thecondenser 13 that cools the water vapor W2 via the cooling fan 46 toconvert the vapor W2 back to the water (condensed water) W1. When thedetection signal output from the liquid level sensor 38, which detects acurrent position of the liquid level 65 that corresponds to the boundarybetween the gaseous-phase portion 70 and the liquid-phase portion 71(see FIG. 10) in the condenser 13, indicates that the position of theliquid level 65 is lower than the lower limit of the predeterminedrange, the control device 60 controls the motor 36 of the return pump 37that supplies water into the condenser 13, to thereby re-supply orreplenish a deficient amount of water from the open tank 32 via the pipe35 to the condenser 13.

Further, when the position of the liquid level 65 is higher than theupper limit of the predetermined range, the control device 60 dischargesan excessive water to the open tank 32 via the intermediate dischargeport 59, air vent 39, etc. In this way, a desirable range of theposition of the liquid level 65 can be set in accordance with the rangedetermined by the lower limit based on the detection by the liquid levelsensor 38 and the upper limit based on the operation of the air vent 39.

The intermediate discharge port 59 for discharging the water (condensedwater) W1 is provided in the intermediate chamber 56 of the condenser13, in order to control the position of the liquid level 65. When theliquid level 65 is higher than the intermediate discharge port 59, theintermediate discharge port 59 causes the water to flow out therethroughto the reserving open tank 32 so that the liquid level 65 can belowered. When the liquid level 65 is lower than the intermediatedischarge port 59, the air vent 39 coupled to the intermediate dischargeport 59 prevents the vapor from escaping via the water outlet 59.

As seen in FIGS. 12-14, the air vent 39 for preventing the vapor fromescaping via the intermediate discharge port 59 automatically closes thevalve when vapor is present in its interior, but automatically opens thevalve when air (non-condensing gas) or water is present.

Further, as seen in FIG. 10, the liquid level sensor 38 is provided at aposition lower than the intermediate discharge port 59, and, when theposition of the liquid level 65 has lowered below the liquid levelsensor 38, a deficient amount of water is re-supplied or replenishedfrom the open tank 32 by means of the return pump 37, so as to raise theliquid level 65 to the position of the liquid level sensor 38.

As set forth above, the position of the liquid level 65 is constantlykept within the vertical range between the intermediate discharge port59 and the liquid level sensor 38. If the interval is distance betweenthe intermediate discharge port 59 and the liquid level sensor 38 isincreased, an error in heat transmission area between the vapor portionW2 and the water (condensed water) portion W1 will become greater.Conversely, if the interval between the intermediate discharge port 59and the liquid level sensor 38 is decreased, the return pump 37 and airvent 39 have to operate very often. Therefore, it is preferable that theinterval between the intermediate discharge port 59 and the liquid levelsensor 38 be set within a moderate range such that both of the above twoadverse influences or inconveniences can be lessened to an appropriatedegree. Further, in order to keep constant the heat transmission areas,it is desirable that the interval between the intermediate dischargeport 59 and the liquid level sensor 38 be as small as possible or zero.

FIG. 16A shows positional relationship among the liquid level sensor 38,the air vent 39 and the liquid level 65 in the Rankine cycle apparatus,and FIG. 16B shows relationship among the liquid level 65 andoperational states of the air vent 39 and return pump 37.

In FIG. 16A, HA, HB and HL represent the upper-limit position of theliquid level, lower-limit liquid level and position of the liquid level65, respectively. When the actual position HL of the liquid level 65 ishigher than the upper-limit position HA, the air vent 39 is set in itsopened position, and the return pump 37 (see FIG. 10) is set in its OFFstate. When the position HL of the liquid level 65 is between theupper-limit and lower-limit positions HA and HB of the liquid level, theair vent 39 is set in its closed position (valve-closed position), andthe return pump 37 is set in its OFF state. When the position HL of theliquid level 65 is lower than the lower-limit positions HB, the air vent39 is set in its closed position, and the return pump 37 is set in itsON state. In this way, variation in the liquid level 65 can be reliablyconfined within the range between the upper-limit and lower-limitpositions HA and HB.

Also, even when the inflow amount (mass flow rate) of water vapor or theamount of water discharge (mass flow rate) to the high-pressure watersupplying pump 44 varies at the time of activation/deactivation ortransient variation of the Rankine cycle apparatus 10, the describedarrangements of the instant embodiment can effectively restrict orcontrol variation of the position of the liquid level 65 within thecondenser 13 and thereby permits stable operation of the condenser 13.

Further, as illustrated in FIG. 10, the Rankine cycle apparatus 10includes the reserving open tank 32 open to the atmosphere and providedseparately from the main circulation circuit. This open tank 32 isconnected to the condenser 13, via the air vent 39 coupled to theintermediate discharge port 59 and the check valve 58. Lower portion ofthe open tank 32 is connected to the outlet port 13 a of the condenser13 via the return pump 37, pipe 35 and check valve 34.

When the liquid level 65 is higher in position than the intermediatedischarge port 59, the water overflows out of the condenser 13 to bedirected into the open tank 32, while, when the liquid level 65 is lowerin position than the liquid level sensor 38, the return pump 37 isactivated to replenish water to the condenser 13. Because the amount ofwater supply by the high-pressure water supplying pump 44, locateddownstream of the condenser 13, is controlled in the instant embodiment,the activation of the return pump 37 causes the liquid level 65 to riseup to the position of the liquid level sensor 38 due to the water supplyinto the condenser 13, upon which the return pump 37 is deactivated.

Further, because the intermediate chamber 56, into which the pluralityof cooling pipes (condensing pipes) 55 open, is provided in the regionincluding the intermediate discharge port 59 and liquid sensor 38, theliquid level 65 is allowed to vary with improved response and in astabilized manner during water discharge from the intermediate dischargeport 59 or water supply from the return pump 37.

Note that the provision of the intermediate chamber 56 is notnecessarily essential to the present invention as long as the vaporintroducing chamber 13A and water collecting chamber 13B are in fluidcommunication with each other via the plurality of cooling pipes(condensing pipes) 55.

Operational sequence of the liquid level position control performed bythe control device 60 is explained below with reference to a flow chartof the FIG. 17.

At step S10, the control device 60 reads the current position HL of theliquid level 65 via the liquid level sensor 38.

At step S11, it is determined whether the liquid level position HL ishigher than the upper-limit position HA of the liquid level, and, if so,control proceeds to step S12, where the air vent 39 is brought to itsopened position to discharge the excessive water so as to lower theliquid level 65. After that, the control device 60 reverts to step S10.When the liquid level position HL is lower than the upper-limit positionHA of the liquid level, control proceeds to step S13 in order to closethe air vent 39.

At step S14, it is determined whether the liquid level position HL islower than the lower-limit position HB of the liquid level, and, if so,control proceeds to step S15, where the return pump 37 is turned on forre-supply or replenishment of deficient water. Further, if the liquidlevel position HL is higher than the lower-limit position HB of theliquid level, the return pump 37 is turned off to not replenish water.After that, the control device 60 reverts to step S10.

FIG. 18 is a timing chart showing variation in the velocity of thevehicle having the Rankine cycle apparatus 10 mounted thereon, variationin the engine output, variation in the amount of water supply to theevaporator and variation in the liquid level position within thecondenser, in contra-distinction to the conventional apparatus. Morespecifically, section (A) of FIG. 18 shows variation in the travelingvelocity of the vehicle, (B) variation in the engine output of thevehicle, (C) variation in the amount of water supply to the evaporatorin the conventional apparatus, (D) variation in the liquid levelposition within the condenser in the conventional apparatus, and (E)variation in the liquid level position within the condenser in theembodiment of the present invention.

As the velocity of the vehicle, having the Rankine cycle apparatusmounted thereon, varies as illustrated in (A) of FIG. 18, the engineoutput of the vehicle varies as illustrated in (B) of FIG. 18, inresponse to which the amount of water supply to the evaporator varies ina manner as illustrated in (C) of FIG. 18 and also the liquid levelposition within the condenser varies in a manner as illustrated in (D)of FIG. 18. In other words, as the vehicle starts traveling at timepoints t1, t3 and t5 and stops traveling at time points t2, t4 and t6along the time axis, the engine output varies and the amount of watersupply to the evaporator also varies, so that the liquid level positionwithin the condenser varies.

With the condenser 100 of the conventional vehicle-mounted Rankine cycleapparatus shown in FIG. 19, the amount of water supply to the evaporator111 varies because the engine output varies as illustrated in (B) ofFIG. 18 in response to the start/stop of the vehicle and transitionalvehicle velocity variation as illustrated in (A) of FIG. 18, so that theliquid level position 112 in the cooling pipes 103 of the condenser 100would vary. Namely, in the condenser 100, the liquid level position 112rises when the inflow amount of vapor is greater than the dischargeamount of condensed water, but falls when the inflow amount of vapor issmaller than the discharge amount of condensed water.

By contrast, according to the instant embodiment, the above-describedliquid level position control is performed when the vehicle varies intraveling velocity as illustrated in (A) of FIG. 18, and thus, theliquid level position can be controlled to vary between the upper-limitand lower-limit positions HA and HB at the time of a start/stop oftraveling of the vehicle. As a consequence, the instant embodiment canreliably prevent great variation or fluctuation in the liquid levelposition within the condenser 13 as illustrated in (E) of FIG. 18.

In the present invention, as set forth above, the positional variationin the liquid level 65 of the water (condensed water) W1 accumulated inthe condenser 13 is confined to the predetermined range, so thatrespective variation of the heat transmission areas of the gaseous-phaseportion and liquid-phase portion, corresponding to vapor and condensedwater, in the condenser 13 can be effectively reduced. As a consequence,the present invention can perform the necessary cooling without regardto variation in the heat transmission areas and achieve an enhancedaccuracy of the control. Also, the present invention can reducecavitations in the pump device and extra heat energy consumption duringre-heating in the evaporator 11.

Further, the present invention can keep a variation width of the heattransmission areas within a permissible range and impart a hysteresis toswitching between discharge and replenishment of the liquid-phaseworking medium, to thereby lower the frequency of the switchingoperation. As a result, the present invention can achieve stabilizedoperation of the condenser 13 and enhanced durability of devicesinvolved in the discharge and replenishment of the liquid-phase workingmedium.

Moreover, because the present invention can appropriately control theliquid level by discharging the liquid-phase working medium (water) fromwithin the condenser 13 while preventing discharge of the gaseous-phaseworking medium (vapor), it can achieve even further stabilized operationof the condenser 13.

Furthermore, the present invention can replenish the liquid-phaseworking medium directly up to the set liquid level from the reservingopen tank, accumulating the liquid-phase working medium, via the returnpump, so that the liquid level position can be appropriately adjustedand accurately stabilized promptly through high-response andhigh-precision supply amount control of the pump.

In addition, the present invention can perform the liquid level positioncontrol while keeping the necessary total mass flow rate of the workingmedium in the circulation circuitry, and thus, the circulation circuitryneed not be equipped with particular devices indented for working mediumdischarge and replenishment to and from the outside.

Furthermore, the present invention can reduce differences in the liquidlevel position among the cooling pipes of the condenser and therebyaccurately stabilize the liquid level promptly during the discharge andreplenishment of the liquid-phase working medium, as a result of whichthe present invention can achieve even further stabilized operation ofthe condenser 13.

Obviously, various minor changes and modifications of the presentinvention are possible in the light of the above teaching. It istherefore to be understood that within the scope of the appended claimsthe invention may be practiced otherwise than as specifically described.

1. A Rankine cycle apparatus constructed into a closed circulationcircuit, which comprises: an evaporator for heating and therebyconverting a liquid-phase working medium into a gaseous-phase workingmedium, using heat from a heat source; an expander for converting heatenergy of the gaseous-phase working medium, discharged by saidevaporator, into mechanical energy; a condenser for cooling and therebyconverting the gaseous-phase working medium, discharged by saidexpander, to the liquid phase; a supply pump for supplying, in apressurized condition, the liquid-phase working medium, discharged bysaid condenser, to said evaporator, and a discharge valve deviceprovided between said supply pump and said evaporator in a portion ofsaid closed circulation circuit where the working medium is in aliquid-phase state, wherein said discharge valve device discharges theworking medium out of said closed circulation circuit when an interiorpressure of said closed circulation circuit is higher than apredetermined limit pressure level that is lower than at least anallowable maximum pressure level of said expander or said evaporator. 2.A Rankine cycle apparatus as claimed in claim 1 wherein at least aportion of the working medium to be discharged out of said closedcirculation circuit via said discharge valve device is discharged aroundthe heat source.
 3. A Rankine cycle apparatus as claimed in claim 1wherein said discharge valve device includes a plurality of dischargepassageways for directing the working medium out of said closedcirculation circuit, and a flow rate limiter is provided in at least oneof said plurality of discharge passageways.
 4. A Rankine cycle apparatusas claimed in claim 1 wherein said discharge valve device is disposed atleast closer to said pump unit than said evaporator.